I. Field of the Invention
The present invention relates to washing machines and more particularly to speed sensors for sensing the speed of rotation of the clothes basket.
II. Description of Prior Art
Washing machines are commonplace in most homes. A typical washing machine includes a drive system having a motor operatively coupled to a drive shaft. The drive shaft includes a first or input shaft which rotates in response to the motor such as via a pulley, clutch and/or brake arrangement. The input shaft is coupled to a transmission having a second or output shaft of the drive shaft, and which in turn supports a clothes basket within a water tub, and an agitator for selective rotation with the clothes basket. In one mode of operation, such as during wash and rinse cycles, the output shaft is caused to rotate back and forth so as to rotate the basket and/or agitator back and forth to thus agitate the clothes and water in the basket for cleaning or rinsing of the clothing. In another mode, such as during the spin cycle, the output shaft spins quickly so as to spin the clothes basket and remove water from the clothing by centrifugal force.
For performance or safety reasons, it is often necessary to monitor the actual speed of rotation of the basket. For example, during the wash or rinse cycles, it may be important to know whether the basket is creeping or spinning. In some cases, whether in the wash or rinse cycle, or in the spin cycle, when the basket is rotating or spinning above a certain speed, it may be desirable to lock the lid closed to prevent someone from sticking their hands into the area of the basket. The speed may also be monitored to determine that the brake has failed, such as where the motor has been deenergized for some time, but the speed sensor continues to indicate that the basket is rotating too fast.
Where speed of rotation is to be detected, the practice has been to employ two part speed sensors. Two part speed sensors typically utilize a magnet and a reed switch (in addition to any magnet and reed switch which might be used to detect whether the lid is opened or closed), neither of which are part of the normal components which are mechanically coupled to and rotate with the drive shaft for proper mechanical rotational operation thereof. Instead, the separate magnet is provided primarily for the purpose of sensing speed and may be mounted for rotation with either the input or output shaft, such as by being taped or otherwise attached to the shaft or to the basket. The separate reed switch is fixedly mounted to a non-rotating part of the machine and adjacent the path of travel of the magnet to detect passage of the magnet during each revolution of the shaft and basket. Passage of the magnet causes changes in the state of the reed switch, resulting in signals from the reed switch over time indicative of the speed of rotation of the shaft and basket. Such two part speed sensors present certain drawbacks, both in terms of cost and reliability.
The present invention provides an improved speed sensor in a washing machine which eliminates the need for a two part sensor and instead relies on a one part speed sensor. To this end, and in accordance with one principle of the present invention, a one part speed sensor is fixedly mounted so as to detect passage of at least one of the components normally mechanically coupled to the drive shaft for rotation therewith to provide proper rotational operation of the shaft(s) and/or clothes basket. In this way, the speed of rotation may be detected by the sensor without the need to add to the shaft and/or basket a second part, such as a magnet, whose primary purpose is to detect speed such as by detection thereof by the sensor. As there is no need to add a second part for the purpose of sensing speed, as opposed to the purpose of providing proper mechanical rotational operation of the shaft, cost is thereby reduced. Additionally, as there is no such second part required, there is no risk of it coming loose, thereby improving reliability. Still further, a one part sensor can be positioned to detect passage of more than one of the components normally associated with the drive shaft for rotation therewith, thereby improving resolution, without the need for additional components. When the normally associated parts are ferrous metal, the one part sensor may be a variable reluctance sensor.
As will be appreciated, normally associated with the drive shaft by being mechanically coupled for rotation therewith are certain necessary metal components which are required to facilitate proper rotation of the shaft and basket from a mechanical perspective. By way of example, the drive shaft has mounted thereto a large metal counterweight and a transmission. The rotation of the counterweight may be detected by positioning a one part variable reluctance sensor adjacent the path of travel thereof to detect its passage on each rotation of the shaft and thereby sense the speed of rotation of the drum. Additionally, the metal screws that are typically part of the corresponding transmission housing may also be detected as they pass such as when the counterweight is out of phase with the sensor, to thereby enhance resolution.
In some washing machines, also mounted to the shaft is a metal brake plate which rotates therewith. The brake plate includes one or more apertures offset from the center thereof for mounting of springs or other components necessary for proper mechanical rotational operation of the drive shaft. A variable reluctance sensor may be positioned to detect passage of the aperture(s) as the shaft spins to thereby detect the speed of rotation of the basket. Where there are multiple such off-center apertures along the path of travel, resolution is enhanced. The shaft may be mounted in the machine by a fixed mounting plate situated in overlying relationship with the brake plate. The sensor may advantageously be mounted to the mounting plate so as to overlie the path of travel of the aperture(s). Where the mounting plate is solid, a sensor aperture may be formed therein over the path of travel with the sensor mounted at or into the sensor aperture.